public class BinarySearchTree {
    static class TreeNode{
        public int val;
        public TreeNode left;
        public TreeNode right;
        public TreeNode(int val){
            this.val=val;
        }
    }
    public TreeNode root=null;
    //查找
    public boolean search(int val){
        TreeNode cur=root;
        while (cur!=null){
            if (cur.val>val){
                cur=cur.left;
            }else if(cur.val<val){
                cur=cur.right;
            }else {
                return true;
            }
        }
return false;
    }

    //插入
    public void insert(int val){
        TreeNode cur=root;
        TreeNode parent=null;
        TreeNode node=new TreeNode(val);
        if (root==null){
            root=node;
            return;
        }
        while (cur!=null) {
            if (val < cur.val) {
                parent=cur;
                cur = cur.left;
            }
            if (val > cur.val) {
                parent = cur;
                cur=cur.right;
            }
        }
        if (val<parent.val){
            parent.left=node;
        }
        if (val>parent.val){
            parent.right=node;
        }
    }
//删除

public void remove(int val){
        TreeNode node=new TreeNode(val);
        TreeNode cur=root;
        TreeNode parent=null;
        while (cur!=null){
            if (cur.val>val){
                parent=cur;
                cur=cur.left;
            }else if (cur.val>val){
                parent=cur;
                cur=cur.right;
            }
            else {
                removeNode(parent,cur);
                return;
            }
        }
}

    private void removeNode(TreeNode parent, TreeNode cur) {
        if (cur.left==null){

            if (cur==root){
                root=root.right;
            }else if (cur==parent.left){
                parent.left=cur.right;
            }else {
                parent.right=cur.right;
            }

        }else if (cur.right==null){
           if (cur==root){
               root=root.left;
           }else if (cur==parent.left){
               parent.left=cur.left;
           }else {
               parent.right=cur.left;
           }


        }else {//最难写，左右都不空
            TreeNode targetParent=cur;
            TreeNode target=cur.right;
            while (target.left!=null){
                targetParent=target;
                target=targetParent.left;
            }
            cur.val=target.val;
            if (target==targetParent.left) {
                targetParent.left = target.right;
            }else {
                targetParent.right=cur.right;
            }
        }
    }


}
